Tag: litografia

In the race to develop ever smaller and better performing chips, several technological limitations need to be overcome. Today, the bottlenecks to continue this trend lie mainly in techniques for manufacturing electronic circuits of less than 10 nanometers (nm). Among the techniques being improved to manufacture the next generation of chips, one of the most promising is extreme ultraviolet lithography (EUVL). This technology takes advantage of the very short wavelength of extreme ultraviolet radiation to pattern nanoscale circuits on the chip with the intermediation of the so-called “resists” – thin layers of radiation sensitive material that cover the chip substrate during nanofabrication.

At the XVI B-MRS Meeting, a plenary lecture will discuss an important contribution that the materials field can make to the next generation of chips: the development of suitable resists for the fabrication of electronic circuits of less than 10 nm through EUVL.

The subject will be presented by Kenneth E. Gonsalves, Distinguished Professor of the Indian Institute of Technology Mandi (IIT Mandi), a teaching and research institution created in 2009, where Gonsalves arrived in 2012 as a visiting professor.

Gonsalves obtained his BS in Chemistry from the University of Delhi (India) followed by an MS also in Chemistry from Boston College (USA) and a PhD from the University of Massachusetts at Amherst (USA) with a doctoral thesis on polymer synthesis. Then he performed a postdoctoral specialization on polymer ceramics at MIT (USA). From 2001 to 2014, Gonsalves was the Celanese Acetate Distinguished Professor of Polymer Materials at the University of North Carolina at Charlotte (USA).

Together with his research group at IIT and his collaborators from the United States, India, Brazil, Taiwan and Europe, Gonsalves carries out research and development on resists for advanced nanofabrication techniques, with support of major companies in the electronics segment, and on polymer scaffolds for tissue engineering.

Here follows a brief interview with the researcher.

B-MRS newsletter: – Tell us a little bit about your main scientific/ technological contributions up to the moment.

Kenneth Gonsalves: – My research has centered on polymers with an emphasis on synthesis of novel materials. For the last 20 years I have focused on resist technology for IC (integrated circuit) fab. This is a fascinating area as it has significant technological applications in the development of integrated circuits, solid state devices. In addition it can also be used successfully for cell and tissue engineering of scaffolds for biotechnologies.

B-MRS newsletter: – About the resists you are working on, what skills and expertise are needed to develop them, in your opinion? When this next generation of chips is expected to be available?

Kenneth Gonsalves: – Resist R&D is multifaceted and extremely complex. It requires extensive collaborations between chemists with organic, inorganic and polymer backgrounds. In addition, interaction with physicists and electrical/electronic engineers is essential. The next generation of chips at the 14 nm node are currently available. Sub 7 nm node technology is expected by 2018 onwards.

B-MRS newsletter: – Describe in the simplest and briefest possible way the process of EUVL, without forgetting to mention the role of resists.

Kenneth Gonsalves: – The EUV photons are generated by a plasma or synchrotron source operating at a wavelength of 13.5 nm. Through a series of special mirrors and a mask, the predesigned template for the IC fab is projected onto photosensitive materials such as polymers as well as inorganics. This is all conducted in vacuum, a challenge for the IC fab industry as it is a drastic change from current photolithography fab, which functions under ambient conditions. The extremely short EUV wavelength is a prerequisite for patterning features at the sub 20 nm scale. The challenges for resists that can meet the sub 7 nm node requirements are enormous. A new paradigm is paramount – hybrid resists, that are partially inorganic may provide solutions to patterning at these scales. Inorganic hardmasks are another alternative. The sensitivity of these photoresists has to be enhanced drastically in order to meet the mass volume production of chips. There are several other critical parameters that have to be met for a successful resist system. Again, this requires multidisciplinary, multi institutional, industry collaboration on a global scale.

In a study led by researchers from Brazil and recently published in Applied Physics Letters (APL), scientists have engraved, on graphene sheets, nanosized periodic patterns, using a new method for that application, the helium hion beam lithography.

The team of scientists used a helium ion microscope (HIM) in order to bombard graphene with these ions and, thus, engrave parallel lines of length 1mm and width of only 5 nm, defining, among them, 20 nm-width ribbons (nanoribbons).

In addition to being quick and simple, the method has proven to be very accurate: it generated point defects smaller than other similar techniques and significantly preserved the atomic structure of the nanoribbons.

The new method extends the application possibilities of graphene, which, it is worth highlighting, is a flat material (it is only one atom tall) composed of densely packed carbon atoms, and which stands out because it can be used in nanoscale and for its high mechanical resistance, great electricity and heat conduction, transparency, and flexibility, among other properties.

“Direct writing in graphene using the focused beams of helium ions allows the fast manufacturing of different devices”, says Braulio Archanjo, researcher at the Brazilian National Institute of Metrology, Quality, and Technology (Inmetro) and lead author of the APL’s article. As an example, Archanjo mentions the possibility of manufacturing, in a near future, in pure graphene, the so-called “PN junctions”, essencial structures in semiconductor devices such as diodes and transistors, widely used in the production of electronics. Today, these structures are basically made in silicon.

AFM topographic image (3D) of graphene surface on SiO2.

The story of the work

In the context of studies on graphene metrology performed in the recent years at Inmetro, reports Archanjo, emerged the idea of manufacturing, in a controlled manner, periodic “defect” patterns, such as the parallel lines of the APL work. In 2012, an Inmetro team, in collaboration with researchers of the Federal University of Minas Gerais (UFMG), published a paper on periodic patterns engraved on graphene using a beam of gallium ions through FIB (focused ion beam) equipment.

Later, in a meeting of Archanjo with professors Carlos Achete, from the Federal University of Rio de Janeiro (UFRJ) and from Inmetro, and Gilberto Medeiros, from UFMG and from the research and development laboratory of Hewlett-Packard (HP Labs), a second work was planned, which would use, instead of FIB equipment, a HIM equipment, which resolution is up to ten times higher, but which is still not available in Brazilian territory.

So Archanjo spent three weeks in Silicon Valley, in the United States, using the HIM of HP Labs to make lithography in graphene samples manufactured at Inmetro. “We brought together the expertise we have here regarding graphene defects with the expertise of the HP Labs researchers regarding using a microscope of focused beams of helium ions”, summarizes the Inmetro researcher.

When he went back to Brazil with several graphene samples with engraved periodic patterns, the team began, at Inmetro, the study of such samples through atomic force microscopy and Raman spectroscopy. “This stage of the work was performed together with professors Benjamin Fragneaud, from the Federal University of Juiz de Fora (UFJF) and Luiz Gustavo Cançado, from UFMG”, tells Archanjo.

HIM: soon in Brazil

In the first semester of 2015, announces Archanjo, Brazil should have its first helium ion microscope. “The experience we gained performing the study at HP Labs will allow us to install it and use it”, says the researcher. The equipment will be available at Inmetro.